Neutral and charged particle detector



Nov. 17, 1970 w. w. HUNT, JR., F-TAL 3,541,331

` NEUTRAL AND CHARGED PARTICLD DETECTOR Filed April 10, 1968 INVENTORS M AWA/7' df:

7'7'0i/Yfy l u Y B 3,541,331 NEUTRAL AND CHARGED PARTICLE DETECTOR William W. Hunt, Jr., Chelmsford, and Kenneth E. McGee, Sudbury, Mass., assignors to the United States of America as represented by the Secretary of the Air Force Filed Apr. 10, 1968, Ser. No. 720,252 Int. Cl. G01t 1/17 U.S. Cl. 250--83 1 Claim ABSTRACT F THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a detector of atomic and molecular particles and more particularly to a transmission type particle detector serving as the active window which feeds electrons into a vacuum sealed electron multiplier in response to external impacts from the particles.

The particle detector may be utilized to improve operation of time-of-ight mass spectrometers in terms of uniformity of response with respect to both time and amplitude and similar improvements in other instruments. Further utilization may be found in detection systems. In addition thereto the particle detector may be used in alphaparticle detection.

The present invention provides a detector of atomic and molecular particles, neutral or charged, ranging in size from H+ upward and in energy from several tens of electron volts upward. Some possible sources of the particles may be ions from a mass spectrometer, molecules from a molecular beam, and alpha particles from radioactive materials.

In the prior art, a particle detector was a device used to indicate the presence of fast moving charged atomic or nuclear particles. When such a particle arrived at a particle detector, it created an electrical disturbance in the detector which can be observed and recorded. Particle detectors are used in research in nuclear and atomic physics and to detect cosmic rays. They are important in exploration for radioactive minerals, since they detect the particles emitted from radioactive substances.

In addition to providing the basic information concerning the presence of a particle, particle detectors may provide much more detailed information. Depending on the detector used information may be obtained on: number traversing detector (counting rate); precise time when particle traversed detector, precise position of particle, energy lost by particle; momentum of particle; and velocity of particle.

The characteristics of particle detectors which are important in determining the type of detector to be used in a given application are speed, proportionality, and the amount of data desired.

United States Patent O ICC The prior art particles detectors have one or more of the following limitations: cathode requires shielding from external light; transit time through detector is dependent upon point of impact; incoming particles travel different path lengths before conversion; long conversion time from particle to light to electrons requires magnetic field; requires external electric field; requires activation procedure after exposure to atmosphere; and difcult to replace, disassemble and re-assemble. The particle detector of the present inventions does not include any of the aboverecited limitations.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a detector of atomic and molecular particles, neutral or charged, ranging in size from H+ upward and in energy from several tens of electron volts upward. It has a transmission type dynode so mounted that it is the window to a sealed volume which contains a high vacuum and electron multiplier. The particles to be detected enter at the window and in turn result in release of electrons on the other side of the window. The resultant electrons are representative of the incoming particles. The electrons are then fed through the vacuum sealed electron multiplier to provide an amplified signal.

Among the unique features of this invention are included the use of a transmission type dynode as an atomic sized neutral or charged particle detector, and the use of this transmission type particle detector as the active window which feeds electrons into a vacuum sealed electron multiplier in response to external impacts from particles.

An object of the present invention is to provide a detector of atomic and molecular particles, neutral or charged.

Another object of the present invention is to provide a detector of atomic and molecular particles, neutral or charged, in which a transmission type dynode is mounted so that it is the window to a sealed volume which contains a high vacuum and an electron multiplier.

Still another object of the present invention is to provide a particle detector which includes a transmission type dynode as the active window which feeds electrons into a vacuum sealed electron multiplier in response to external impacts by the particle upon the window.

The various features of novelty which characterize this invention are pointed out with particu-larity in the claims annexed to and forming part of this specification. For a better understanding of the invention, however, its :advantages and specific objects obtained with its use, reference should be had to the accompanying drawings and descriptive matter in which lis illustrated and ldescribed a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Of the drawings:

FIG. 1 shows a preferred embodiment of the particle detector of the present invention;

FIG. 2 shows a fragmentary left end view of FIG. 1;

FIG. 3 shows a right end view of FIG. l;

FIG. 4 is an end view of metallized plastic disc included in FIG. 1;

FIG. 5 is an end view of the metal foil utilized as the grid includes in FIG. 1;

FIG. 6 is an end view of the stainless steel ring included in FIG. 1; and

3 FIG. 7 is a side view of FIGS. 4, 5, and 6, respectively, prior to their assembly with arrows indicating the directionof their assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to FIG. 1, there is shown assembly 14 which includes plastic disc 11, grid structure 12, and stainless steel ring 13. Plastic disc 11 is provided with outer gold coating 11a and inner gold coating 11b. These gold coatings may be applied in any of several conventional methods, for example, by vacuum evaporation. These gold coatings 11a and 11b for plastic disc 11 are indicated in` FIG. 7.

Now referring to FIG. 5, there is shown a front View of stainless steel foil which is subsequently welded around its outer circumference to stepped stainless steel ring 13 of FIG. 6. After welding, it is then etched in a conventional manner to form screen grid 12a, as shown in FIG. 2. Screen grid 12a is ninety percent transparent to permit electron flow therethrough. Ihere is also shown a front view of plastic disc 11 with outer gold coating 11a at FIG. 4.

Now referring to FIG. 7, there is shown side views of plastic disc 11 having inner and outer gold coatings 11a and 11b, respectively, grid structure 12, and stepped stainless steel ring 13, respectively, which are assembled in the direction indicated by the arrows. As previously stated, grid structure 12 is Welded to stepped stainless steel ring 13 and thereafter metallized disc 11 is placed adjacent thereto and making electrical contact thereto. There is thus provide assembly 14, as indicated at FIG. 1 and FIG. 2.

Referring once again to FIG. 1, assembly 14 is shown placed in glass envelope 15 so that the left end of glass envelope is pressure tted into the stepped portion of stainless steel ring 13. Assembly 14 provides extraordinary structural strength and electrical stability to the element enclosed therein. `Glass seal ring 17 is applied around the outer circumference in such manner that it includes disc 11grid structure 12, and stepped stainless steel ring 13 so as to form a vacuum tight seal of assembly 14 and glass envelope 15. It is to be noted that in place of glass envelope 15 there may be substituted a metal envelope.

Lead 19 is connected to stepped steel ring 13. Since grid structure 12 is welded to stepped ring 13 and gold coat 11b is in electrical contact with grid structure 12, lead 19 provides electrical contact to gold coat 11b, grid structure 12, and stepped stainless ring 13. Lead 19 is connected to pin 20 which is brought through glass envelope 15 in such a manner as to be vacuum tight thereat. Pin 20 is connected to source of positive potential 21. The magnitude of the positive potential is one conventionally utilized in directing the flow of hereinbefore described charged particles.

There is also provided electron multiplier 16 being so disposed that a signal may be received for ampliiication at input 16a. Input 16a is additionally arranged to be approximately parallel and in closeV proximity to stainless steel ring 13 (for example, about .015 of an inch). There is also shown at the right end of glass envelope 15 pins interconnecting the electrodes of electron multiplier 16 to power source 22 xwhich provides the requisite operating voltage therefor. IPin 23 is provided for connecting the output electrode of electron multiplier 1'6 to output terminal 24.

After disposing electron multiplier 16 in glass envelope 15 and arranging the pins at the right end thereof in such manner as to be vacuum tight as indicated at right end view of FIG. 3, glass envelope 15 is evacuated and then sealed at point 18. It is to be noted that electron multiplier 16 is conventional and may be such as described at pages 580 and 581 of Van Nostrand Scientific Encyclopedia, Third Edition, published in 1958 by D. Van Nostrand Company, Inc. It is noted that the aforementioned power source 22 utilized with conventional electron multiplier 16 supplies only the electrodes of the aforesaid multiplier with the 4 conventional potentials whereas as previously described source of positive potential 23 supplies the conventional voltage to gold coat 11b, gold structure 12 and stepped ring 13.

In the operation of the preferred embodiment of the invention shown at FIG. l, incoming atomic and molecular particles, neutral or charged, ranging in size from H+ upward and in energy from several tens of electron volts upward are directed toward gold coat 11a as indicated by the arrows. When the particles impinge on the outer surface of gold coat 11a, electrons are emitted from the rear surface thereof in response thereto. A gold coat or layer has inherent characteristic therein the .property of emitting electrons in response to particle impingement. Any -metal coat or layer may also be utilized that has this inherent characteristic. This mode of operation of gold coat 11a may be also termed transmission type dynode. These electrons are attracted by a positive potential applied to gold coat 11b. Thus, the released electrons pass through plastic disc 11 and impinge on the outer surface of gold coat 11b which in turn emit electrons from inner surface thereof. Because of the positive potential applied to screen grid 12a which is ninety percent transparent, the emitted electrons from inner surface of gold coat 11b are directed therethrough and are attracted to input 16b of electron multiplier 16 by reason of the positive potentials which are present in the conventional operation of an electron multiplier. The multiplied signal appears at the output terminal 24 at a level suitable for handling. The mutiplied signal output is then representative of the incoming particles and thus a particle detector is provided. It is emphasized that gold coating 11b may be omitted and that with only gold coat 11a, particles will be detected also in the same manner as previously described. However, there will be only a single impingement of particles and a single release of electrons in response thereto. The electrons will then be directed through plastic disc 11, screen grid 12a and stainless steel ring 13 to input 16b of electron multiplier 16 which will then provide a multiplied signal atoutput terminal 24.

It is emphasized that the preferred embodiment will detect atomic or molecular particles,` charged or neutral and provides improved operation in terms of uniformity of response with respect to time and amplitude.

It is further noted that the preferred embodiment includes a transmission type dynode so mounted that it is the window to a sealed volume which contains a high vacuum and an electron multiplier.

Accordingly, while a particular embodiment of the invention has been shown, it will be understood that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall Within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patents is:

1. A detector of atmoic and nuclear particles, neutral and charged, comprising a first layer of gold, said first layer having an outer surface and an opposite, adjacent inner surface, said particles to be detected impinging on said'outer surface and resulting in a corresponding emission of electrons from said inner surface, a plastic disc having inner and outer surfaces, said outer surface supporting said first layer, a second layer of gold also having an outer surface and an opposite, adjacent inner surface, with said second layer being supported on said inner surface of said plastic disc, a grid structure adjacent to said second layer, a stepped stainless steelring, said grid structure being integrated and welded to said stepped stainless steel ring, a source of positive potential electrically connected to said stepped stainless steel ring, said grid structure and said second layer of gold, said electron emission from said inner surface of said iirstlayer of gold being directed by said positive potential through said plastic disc to said outer surface of said second layer of gold thus operating to emit further electrons from said inner surface of said second layer of gold with a further corresponding emission of electrons being directed through said grid structure, an evacuated container having inner and outer ends with said stepped stainless steel ring pressure fitted to said inner end, and an electron multiplier having an input and output with said input being adjacent to said stepped stainless steel ring and said output disposed at said outer end of said container, said electron multiplier being included in said evacuated container, said electron multiplier receiving at the input thereof the electrons directed through said grid structure and operating to provide an ampliied output signal representative of said impinging particles.

References Cited UNITED STATES PATENTS RALPH G. NILSON, Primary Examiner M. J. FROME, Assistant Examiner U.S. Cl. XR. 

